The invention relates to improvements in a device for atomizing liquid with the aid of gas, or for comminuting gas into small bubbles with the aid of liquid, wherein the gas and the liquid are joined into a two-phase mixture in a mixing chamber and mixed, and wherein the inflow speeds and the volumetric flows of the various phases are selected, taking into account the status variables of the resultant two-phase mixture in view of the outflow cross section of the mixing chamber, such that the outflow speed of the two-phase mixture is approximately equal to the characteristic sonic velocity of the two-phase mixture, and the two-phase mixture leaves the mixing chamber with an abrupt pressure reduction.
A mixing device of this kind is known in the prior art from German Patent 26 27 880. The prior art device is distinguished by effective atomization of liquids or comminution of gas into many small bubbles with little expenditure of energy. The following discussion refers only to the atomization of liquids, but the invention is equally suitable for the comminution of gases.
In many fields of process technology, such as in drying technology or combustion technology, atomization devices for liquids are needed. Usually, mass transfer and/or heat exchange takes place between the atomized liquid and a gas. To this end, the liquid must be atomized as finely as possible, in order to attain a large phase boundary surface between the two substances.
In certain applications of the nozzle according to the invention, such as chemical desulfurizing of flue gas with milk of lime or cooling flue gas with injected water, the problem that arises is that the quantities of gas to be handled fluctuate severely. As a result, the amount of water to be atomized and needed for this purpose undergoes correspondingly severe fluctuations.
Experiments by the present applicant have shown, in the case of partial-load operation described, that the consumption of propellant gas increases sharply if the liquid quantity is reduced. This is likely to be due to the fact that the reduced throughput of liquid in the nozzle opens up a free cross section that is then filled up by the gas component.
Although a plurality of smaller-sized nozzles can be used to reduce the gas consumption in partial load operation, and can then be switched on or off as needed, nevertheless this process is very expensive because of the numerous nozzles required; nor can it be used in all cases.
If an attempt is made to reduce the gas pressure upstream of the nozzle and thereby reduce the gas consumption, relatively coarse atomization ensues, which is undesirable from a reaction standpoint. Furthermore, means for keeping the various pressure levels constant are needed, and so once again this method is expensive.